Cosecant squared antenna-reflector systems



March 21, 1961 c. c. CUTLER COSECANT SQUARED ANTENNA-REFLECTOR SYSTEMSFiled March 24, 1949 5 Sheets-Sheet 1 DEGREES OFFAX/S 2015 IO 5 o 5 IO2o so 354045 i is INl ENTOR By C. C. CUTLER A T TORNEV March 21, 1961 c.c. CUTLER COSECANT SQUARED ANTENNA-REFLECTOR SYSTEMS 5 Sheets-Sheet 2Filed March 24, 1949 5 IO I5 20 25 3035 4045 50 DEGREES OFFAXIS UP IATTORNEY March 21, 1961 c. c. CUTLER COSECANT SQUARED ANTENNA-REFLECTORSYSTEMS 3 Sheets-Sheet 3 Filed March 24, 1949 INVENTOR CC. CUTLER BY QATTORNEY d tates fPt COSECANT SQUARED ANTENNA-REFLECTOR SYSTEMS Filed24, 1949, Ser. No. 83,108

10 Claims. (Cl. 343-779) This invention relates to antenna-reflectorsystems and particularly to directive cosecant antenna reflector sys- Asis known, in an antenna system comprising a main paraboloidal reflectorand a conventional primary antenna or feed at the reflector focus, aso-called cosecant directive pattern may be obtained by modifying theshape of the main reflector. Also, as is disclosed in my copendingapplication, Serial No. 547,399, filed July 31, 1944, which matured intoUnited States Patent 2,489,865, granted November 29, 1949, the cosecantpattern may be obtained by equipping the reflector with one or moreproperly positioned auxiliary strip reflectors. Modifying theparaboloidal reflector or adding thereto auxiliary reflectors involvesmanufacturing difliculties, and for this and other reasons, it nowappears desirable to obtain a cosecant antenna system comprising aconventional paraboloidal reflector and a primary antenna adapted tosecure, in conjunction with the main reflector, the desired cosecantfield distribution.

It is an object of this invention to obtain a highly satisfactorycosecant directive pattern.

It is another object of this invention to obtain, in anantenna-reflector system, a cosecant pattern utilizing a conventionalparaboloidal reflector.

It is still another object of this invention to obtain a simple,inexpensive and easily manufactured cosecant antenna-reflector system.

In accordance with the preferred embodiment of the invention the antennasystem comprises a standard paraboloidal main reflector, the axis of thereflector being prising a dual-aperture wave guide at the reflectorfocus, and a plurality of auxiliary reflectors positioned above thefocus and having convex reflective surfaces facing the upper half of themain reflector. In operation, the primary antenna illuminates orenergizes the entire main reflector. A portion of the energy reflectedby the upper half of the main reflector impinges upon the auxiliaryreflectors and is redirected to the main reflector and thence in adownward direction through the focus, whereby a cosecant pattern in thevertical plane is obtained. In the horizontal plane the pattern issymmetrical about the reflector axis.

The invention will be more fully understood from a perusal of thefollowing specification taken in conjunction with the drawings on whichlike reference characters denote elements of similar function and onwhich:

Fig. 1 is a side view, Fig. 2 a top view and Fig. 3 a partialperspective view of one embodiment of the invention;

Fig. 4 isa measured cosecant pattern for the embodiment of Figs. 1, 2and 3;

Fig. 5 is a side view, Fig. 6 a top view, and Fig. 7

a partial perspective view of a different embodiment of the invention;

Fig. 8 is a diagram used for explaining the operation of the embodimentof Figs. 5, 6 and 7;

normally horizontal, a primary antenna therefor com- Fee Fig. 9 is ameasured cosecant pattern for the embodiment of Figs. 5, 6 and 7;

Fig. 10 is a side view and Fig. 11 a partial perspective View of anotherembodiment of the invention;

Fig. 12 is a diagram used in explaining the embodiment of Figs. 10 and11;

Fig. 13 is a side view and Fig. 14 a partial perspective view of stillanother embodiment of the invention; and

Fig. 15 is a diagram for explaining the operation of the embodiment ofFigs. 13 and 14.

Referring to Figs. 1, 2 and 3 the antenna system comprises a mainconventional paraboloidal reflector or sec ondary antenna 1 and aprimary antenna 2 of the socalled rear-feed wave guide type. The mainreflector 1 is concave and has a circular periphery, an axis 3, a pointfocus 4 and a vertex section or region 5. The primary antenna 2comprises a head 6 having two antenna orifices 7 facing the reflector 1and a rectangular wave guide 8 connecting the head 6 to a translationdevice 9 and passing through the reflector vertex 5. The focus 4 ispositioned about midway between the two orifices 7. The device 9 may bea transmitter or a receiver or a combined radar transmitter-receivercommonly known as a transceiver. As described so far the system is thesame as that illustrated by Fig. 3 of my Patent 2,422,184, granted June17, 1947.

In accordance with the present invention an array 10,

comprising three convex reflectors 11, 12 and 13, is

positioned entirely above the axis 3, of the concave reflector 1, in amanner such that the three convex reflecting surfaces face the concavereflecting surface of the main paraboloidal reflector 1. The threereflectors 11, 12 and 13 are supported by the vertical members 14 whichare fastened to each other by the rivets or bolts 15 and attached to thehead 6. As illustrated on the drawing,

,mately equal horizontal dimensions and the horizontal .dimension ofreflector '11 is greater than that of reflector 12 or 13. The radii ofthe'cylinders' corresponding to reflectors 1'2 and 13 are approximatelyequal and the radius of the cylinder corresponding to the reflector 11is greater than that of the cylinder corresponding to reflector 12 or13.

In operation, assuming the device 9 is a transmitter, waves having ahorizontal electric polarization are supplied by device 9 over guide 8to the head 6 and then propagated through the two orifices 7 and alongdiverging paths 17 towards the concave reflector 1. As is known,considering the vertical plane, Fig. 1, the wavelets or rays areredirected by the paraboloidal reflector 1 along paths, such as thepaths 18, parallel to the axis 3. A portion of the energy reflected bythe upper half of the reflector impinges upon the convex reflectors 11,12 and 13, and is returned to the upper half of the concave reflectoralong the parallel paths 19. The returned wavelets are then redirectedby the concave reflector along the downwardly pointing directions 20. Asa result, the radiation in the vertical plane is unsymmetrical about thereflector axis 3 and, assuming the antenna system is installed on anaircraft, the radiation in directions extending upwards from the axis 3,the so-called sky radiation, is relatively small whereas the radiationin directions extending downwards from the axis 3, the 'socalled grounradiation, is relatively large, whereby irises are well known in theart.

a satisfactory cosecant pattern in the vertical plane is obtained. Thus,referring to Fig. 4, the full line curve 21 illustrates a measuredvertical of H-plane consecant pattern for a system constructed inaccordance with Figs. 1, 2 and 3. The dash-dash curve 22 illustrates thetheoretical or optimum cosecant pattern. In the E or horizontal planeall the wavelets are redirected by the concave reflector 1 along theparallel paths 18 and the pattern is symmetrical about the reflectoraxis 3. In reception the converse operation is obtained.

Referring to Figs. 5, 6, 7 the primary antenna or cosecant feed 23 forthe standard reflector 1 comprises a non-square rectangular wave guide24 having a longitudinal parabolic curvature 16, corresponding to thecontour of reflector 1, and a rear-feed bent non-square rectangular waveguide 25 having one end connected to the translation device 9 and theother end connected by the flange assembly 26 to the top end of theparabolic guide 24. The narrow walls of the guides 24 and 25 areparallel to the electric polarization 27 of the waves utilized. A narrowor E-plane wall of the parabolic guide 24 faces the reflector andcontains a principal antenna aperture or iris 28, a set of alternatecapacitive irises 29, 30 and a set of alternate inductive irises 31, 32.The principal iris 28 is positioned at the focus 4 of reflector 1 andthe remaining iris are positioned above the axis 3 of the reflector.

It may be noted here that inductive and capacitive Thus, for example, ifan iris is formed inside a non-square rectangular guide by a pair ofspaced conductive members extending between and connecting the H-planeor wide walls (perpendicular to the electric polarization) the iris isinductive, whereas if the members extend between, but do not connect,

the E-plane walls (parallel to the electric polarization) the iris is'capacitive. As shown on the drawing the capacitive iris has an I-shapedopening.

In operation, assuming the device 9 is a transmitter,

waves emitted by the principal iris 28 illuminate the enpaths 18.Considering the vertical plane, Fig. 5, wavelets emitted by thesubsidiary irises 29, 30, 31 and 32 are cophasal and in phase with thewavelets from the principal iris 28, as explained below, and thesewavelets for the most part travel along the parallel paths 33 and, afterimpinging upon the upper half of the concave reflector 1, arepropagatedthrough the focus 4 and along the downward directions 34, whereby in thevertical plane a cosecant pattern is secured, as in the system of Figs.1, 2 and 3. Thus, the curve 35, Fig. 9, illustrates the measuredvertical plane cosecant pattern obtained for a system constructed inaccordance with Figs. '5, 6 and 7. The curve 36 of .Fig. 9 illustratesthe optimum cosecant curve. By reason of the parabolic contour of theguide 24 the energy distribution or illumination of the reflector 1 isthe optimum. In the horizontal plane, Fig. 6, the pattern is symmetricalabove the reflector axis 3, as in the system of Figs. 1, 2 and 3.

The wavelets from the five irises 28, 29, 30, '31 and 32 are renderedcophasal by judiciously positioning these irises so that the time,consumed by a wavelet in traveling from a given point or reference:position of the wave front 37, Fig. 8, in the guide 24 through theassociated iris to the vertical plane 38 perpendicular to the reflectoraxis 3, is equal to the time consumed by a wavelet in traveling from thewave front reference position 37 through the adjacent iris to the wavefront reference position 33 minus a full cycle, that is, 360 degrees,the 90 degree phase delay or advance in each iris being, of course,taken into consideration. In Fig. 8, the distances from the wave frontreference position 37 in the guide to the five irises are designated bythe letter L with subscripts I to 5, respectively, as shown, thewavelength in the guide A being added to the designations to indicatethat throughout each of these distances,

the energy has the wavelength A Similarly, the distances from each ofthe five irises to the reference plane 38 are designated by the letter Dwith subscripts 1 to S for the five irises, respectively, as shown, thewavelength in free space h being added to the designations to indicatethat throughout each of these distances, the energy has the wavelengthM. More particularly, the time, T

in degrees for the wavelet passing through the inductive iris 32 andtraveling from the front 37 to the plane 38,

may be represented where:

k is the wavelength in centimeters in guide 24,

A is the wavelength in centimeters in free space,

L is the distance in centimeters from the wave front 37 to the iris 32,

D is the distance in centimeters from the iris 32 to the plane 38, and

(+) represents the degrees of phase delay passing through the inductiveiris 32.

The adjacent iris 30 is spaced from the iris 32 a dis tance such thatthe time, T for the wavelet passing through iris 3t? and traveling fromthe front 37 to the plane 38 is where:

L is the distance from front 37 to iris 30,

D is the distance from iris 30 to the plane 38, and

(-90) represents the degrees of phase advance produced by the capacitiveiris 30.

Now, in order to produce cophasal wavelets at the plane 38 we have From(1), (2) and (3) we have L2 & l Q 22 Kg- \r M e (4) p (la-Dar. L2 L1- 2M (5l Letting S represent the spacing between the mid-points of irises30 and 32 and R the ditference between the lengths of the paths D and Dwe have Similarly for irises 31 and 30 23=%-+ Ri -1 (a where S is thedistance between the mid-points of irises 31 and 3t) and R is thedifference between the lengths of the paths D and D In a similar mannerthe positions of the irises 29 and 28 may be determined.

The system of Figs. 10, 11 and 12 is the same as that of Figs. 5, 6 and7 except that a linear feed guide 39 is used in place of the parabolicfeed guide 24. As shown in Fig. 12 the adjacent capacitive and inductiveirises are spaced 2 half guide wavelength apart, whereby all of theoutgoing wavelets are cophasal. The arrows 40 illustrate the phases ofthe wavelets inside the guide at the iris locations and the arrows 41illustrate the similar phases of the outgoing Wavelets. The operationinboth planes is the same as that of the system of Figs. 5, .6 and 7except that the distribution produced by the linear feed 39 is not assatisfactory as that produced by the parabolic feed guide 24. In thehorizontal plane a symmetrical pattern is secured.

The system of Figs. 13, 14 and is the same as that of Figs. 10, 11 and12 except that the irises 28, 29, 30, 31 and 32 of guide 39 are spacedso as to focus the wavelets in the region of the vertex 5 of thereflector 1, as shown by the paths 42, whereby the vertexregionfunctions in a sense as a plane reflector and the downward radiation isenhanced as illustrated by the arrows 43. In a manner similar to thatexplained in connection with Fig. 8, the irises 28, 29, 3t), 31 and 32are judiciously positioned so as to secure the focussing effect. Thus,referring to Fig. 15, the Equations 1 to 7 given above apply when D D DD and D denote the distances in centimeters from the vertex 5 to theirises 28, 2Q, 30, 31 and 32, respectively. By virtue of the focussingeffect described above a cosecant pattern is obtained in the verticalplane. In the horizontal plane a symmetrical pattern is secured. In Fig.15, the paths in the guide are designated L with subscripts 1 to 5,inclusive, and the paths in free space are designated D with subscripts1 to 5, inclusive, and the wavelengths k and A are indicated in the samemanner as explained in connection with Fig. 8, above.

Although the invention has been explained in connection with certainembodiments it is not to be limited to the described embodiments sinceother apparatus may be successfully utilized in practicing theinvention.

What is claimed is:

1. An antenna-reflector system for producing a cosecant directivepattern comprising a paraboloidal reflector, a primary antenna thereforcomprising a wave guide extending longitudinally across the front ofsaid reflector and having a plurality of irises facing said reflectorsaid wave guide being positioned substantially on one side only of theaxis of said reflector.

2. A system in accordance with claim 1, said guide having a paraboliclongitudinal curvature corresponding to the parabolic curvature of saidreflector.

3. A system in accordance with claim 1, said guide being linear and thespacing between adjacent irises being a half guide wavelength.

4. A system in accordance with claim 1, said guide being linear and thespacing between adjacent irises being a function of the guide wavelengthand the difference in the distances between said focal point of saidreflector and said irises.

5. A system in accordance with claim 1, said irises being located alonga line, one set of alternate irises having an inductive reactance andthe other set of alternate irises having a capacitive reactance.

6. A system in accordance with claim 1, said guide having a paraboliccurvature, the spacing between adjacent irises being a function of theguide wavelength and the diflerence in the distances from said irises toa plane perpendicular to the axis of said reflector.

7. An antenna-reflector system for producing a cosecant directivepattern comprising a paraboloidal reflector and a primary antennatherefor, said primary antenna comprising a wave guide closed at one endextending across the front of said reflector, said primary antennahaving a main iris near the closed end of said wave guide, said mainiris being positioned on the axis of said reflector, said primaryantenna having a plurality of secondary irises at progressivelyincreasing distances from the closed end of said wave guide, all of saidirises facing said reflector.

8. A system in accordance with claim 7, said guide having a paraboliclongitudinal curvature corresponding to the curvature of said reflector.

9. A system in accordance with claim 7, said guide being linear and thespacing between adjacent irises being a function of the guide wavelengthand the differonce in the distances between said focal point of saidreflector and said irises.

10. A system in accordance with claim 7, said irises being located alonga line, one set of alternate irises having an inductive reactance andthe other set of alternate irises having a capacitive reactance.

References Cited in the file of this patent UNITED STATES PATENTS1,771,148 Sprague July 22, 1930 2,342,721 Boerner Feb. 29, 19442,436,380 Cutler Feb. 24, 1948

